Electrical Engineering

Questions tagged [fft]

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FFT is an acronym for Fast Fourier Transform. Use this tag for FFT-related questions. Try to also select a specific chip or software tag when possible.

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Arduino FFT on data received from current sensor

I'm working on a project of a predictive maintenance application, where I would like to sample an alternate 50 Hz current by sensors based on the Hall effect (such as ACS712 or any sensors with a ...
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53 views

Is it possible to do an FFT on the output of a 4 bit ADC?

I made a simple 4 bit flash ADC on a breadboard, and I want to run an fft on the output. Is it possible to do an FFT on data that is only 4 bits in resolution.
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The effects of frequency resolution in FFT on the frequency spectrum

This is a section for the parameter study of my thesis (basically: why and how I did what I did in the experiments). Currently, I have to choose the fit bandwidth and FFT lines combination for the ...
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60 views

Simple FFT with DSP on STM32F407VG: How to interpret results and clear noise

It's my first project with STM32 (board stm32f4-disc1). I'm trying to create a simple spectrum analyzer for analyzing a signal (400-7000Hz, 0-3000 mV). My goal is to catch an event when the signal is ...
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36 views

How can I see the magnitude and frequency of a signal (DFT) in PLECS?

I am trying to obtain the Fourier transform of a signal by using the DFT of PLECS but I got some weird results. Here is a very simple sinewave generator and the DFT block: DFT_plecs_1 Here are the ...
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40 views

Frequency of a load curve signal

I have measured a charge and discharge curve of a capacitor with resistor and I want to calculate the frequency of this signal (for a low pass filter). Am I on the right way if I calculate 1 divided ...
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68 views

Overtones(?) seem to be showing up in FFT of audio signal

I am processing audio data using a Teensy 3.2. I have a microphone attached to it, and am playing music in my room using some powerful speakers. When I look at data from the Fourier Transform of the ...
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2answers
90 views

Bucketing FFT into one-third octave bands

I'm trying to understand how to take the results of an FFT calculation and bin them to one-third octave bands. As my questions aren't about the code but about fundamentally understanding the arguments ...
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15 views

FFT Power Spectrum and PDS - Max Hold

I have a problem with FFT Power Spectrum and PDS VI - I would like to see the max hold values displayed on the spectrum, but the only options in the cluster "averaging parameters" are "...
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2answers
148 views

Relation between Fast Fourier Transform and Laplace/Continuous Fourier representation

I am trying to identify a system by means of its differential equation (i.e., Lapace representation). I put together a rather straightforward regression algorithm (similar to Proni's method for ARMA) ...
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1answer
130 views

FFT of time-compressed signal not outputting correct amplitude spectrum

Given a signal g(t) <--> G(f), a time-compression g(at) <--> 1/(abs(a)) * G(f/abs(a)), but not with the FFT as I've found out. Performing the FFT on g(a*t) doesn't scale the amplitude of ...
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67 views

Low-pass filter on PDM data provides data that does not have a FFT

I'm trying to convert PDM data into analog form by passing the data through a low-pass filter in Matlab. My approach is fairly simple and matches the answer given in this Electrical Engineering Stack ...
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35 views

FFT Frequency Bin - Impact on Energy Totals

If I reduce the number of samples used for an FFT (increasing the width of the frequency bins), is it correct to say that the energy in two bins with smaller frequency bins (eg. 10kHz-20kHz and 20kHz-...
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84 views

Calculate receiver dynamic range (understanding the effect of FFT processing gain)

I'm attempting calculate the dynamic range of a receiver. That is, the ratio between the maximum and minimum detectable powers at the reception antenna. The receiver is composed of (in order) an ...
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1answer
37 views

FMCW - FFT - Range resolution

with a prototype of FMCW radar I'm trying to resolve the distance to the target The Audio card characteristics are as follows: Fs= 44100Hz So the FMCW radar range resolution is RR=440MHz/c = 0.34m Ts=...
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1answer
39 views

Negative Freqs from FFT in Laplace Circuit Analysis

Do I use the absolute-value of the FFT frequencies when using the Laplace equations for calculating the impedance of an RLC circuit? I'm currently working on something where I need to numerically ...
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1answer
270 views

FM demodulator LTspice

I am now designing an FM demodulator circuit. And the first step is turning FM into AM, so I could use envelope detector afterwards. Modulator circuit is designed using Colpitts topology. So frequency ...
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64 views

Would unstable sample rate affect spectrum after FFT?

The system samples analog input and then conduct FFT on the samples and then display the spectrum. Currently, the issue is the displayed spectrum line position is keeping shift between each scan. ...
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103 views

How are the neat sinc function shaped carriers produced in OFDM?

I am learning about OFDM and QAM. Every explanation I have read illustrates how the separate carriers are sinc functions that are arranged to overlap in a nice orthogonal way so as to cancel out ...
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1answer
67 views

Strange currents in a lathe

I am playing with MCSA and Park's Vectors to value motors' health. As test bed I read currents out of a lathe Spinner TC600, and see something strange: Park's diagram is a snowflake (instead of an ...
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24 views

FFT Simulation Arduino Due

I am writing a report for a prosthesis design. In one of the parts of the design, I am using the FFT to classify slip. I want to do a simple simulation to show the use of the algorithm I am using, ...
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1answer
49 views

How do I approximate number of calculations/operations/memory/hardware is required for a 2^18 point FFT on chip?

I am looking for FFT implementation on Chip/FPGA. I need a high-resolution FFT which is a minimum of 2^18 points. However, I need to approximate how much hardware will I require for this process. I ...
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53 views

FFT of R2R DAC in LTSpice

I designed a 6-bit current-mode R2R DAC in LTSpice. This is the output spectrum with a 500kHz input sinusoid to an ideal ADC (running at 10MHz clock) which feeds directly into the DAC. Vin is input to ...
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79 views

Handheld oscilloscope for saving waveform in memory [closed]

I am looking for an handheld oscilloscope which can save some single frozen waveforms on memory and transfer it later to a computer. The saved waveform should have a lot of points so that I can ...
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16 views

Discrete Cosine Transform (DCT) Coefficient Distribution

I have two images : Original Image Binarized Image I have applied Discrete Cosine Transform to the two images by dividing the 256x256 image into 8x8 blocks. After, I want to compare their DCT ...
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4answers
216 views

FFT of a square wave

I'm generating a square wave as PWM whose frequency is set to 25 Hz. On the oscilloscope, I've got: The data referred to the image above was stored and maniputed, then I plot it using jupyter ...
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1answer
57 views

Quantization results in harmonics in ADC FFT plot

This is taken from Analog-to-Digital Conversion by Marcel Pelgrom. Okay, I understand that with 1-bit quantization, the output is block-wave (Square) and that of course when you do the Fourier Series,...
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72 views

FFT in oscilloscope measuring Frequency spectrum

I am using a Keysight InfiniiVision MSOX3054T Scope having Bandwidth of 500MHz and Sampling rate of 5Gsa/s. I am learning to use the FFT Option in the scope. Below is the waveform I captured of my ...
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50 views

Fourierspectrum of the output voltage of an real inverting amplifier

First a quick descripton of my circuit: The inverting amplifier amplifies by 20dB, the input voltage is a sinus signal with the Frequency 10 kHz and the peak to peak voltage is 200mV or 10V. The used ...
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46 views

Estimating FFT error

I'm interested in trying to estimate the worst-case error when using a particular DFT implementation (CMSIS) and an ADC and voltage reference with known error bounds. I think that I can work out the ...
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1answer
104 views

Using an FFT to identify noise

First off, please note that I am a hobbyist. I have a couple of line level audio outputs that are picking up noise from a nearby 12v signal anytime it pulses. These pulses are translating into ...
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59 views

Sampling Frequency of a pulsed radar signal

I'm new to radar. please excuse my question if it doesn't make sense to you. In a pulsed radar signal, why is the required sampling frequency "2 times the inverse of pulse width" instead of "2 times ...
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2answers
170 views

How to interpret the FFT of the mains voltage in this case?

I coupled the 230Vrms AC mains voltage to a scope channel through a 10Vpk-pk step-down transformer. I can imagine the transformer will already filter high freq. noise but I thought I can still see ...
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161 views

PSD vs FFT of voltage magnitude squared and oscilloscopes

Imagine we have a time-domain signal which is a voltage signal. Now if we sample this at the correct rate, and taking the Fourier transform gives us the magnitudes of various frequency components ...
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2answers
130 views

Guitar to MIDI conversion

I am wanting to measure the pitch of a single guitar string and convert into MIDI within 10ms. FFT takes too much time, I was wondering what other options are worth looking at? The main issue is ...
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1answer
61 views

How to see Signal frequency and Sampling frequency on the frequency spectrum

If I have a 100 Hz periodic analog signal and let us say it is band limited to 1kHz and I sample it at 3 kHz. If I want to see its frequency spectrum then how to differentiate between the signal ...
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122 views

Can we use both FFT and PSD to obtain a random signal's frequency domain representation?

I always encounter random noise frequency domain representation as PSD(not FFT), something like in the below plot: Without diving into math too much, practically speaking can we always use FFT ...
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64 views

DIY high fidelity audio using delta sigma adc

This question may be too general, but I will include all the details that I can. My end goal is to achieve a super high-resolution spectrogram of any recording I choose to make. By doing some tests I ...
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1answer
86 views

Decoding Signals from an Unknown Port on Spectrometer

We have a Thermo-Nicolet Nexus 670 FT-IR Spectrophotometer, made in the USA around 2000. It was the work horse of the infrared spectroscopy community. The instrument sends out signals to a proprietary ...
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1answer
88 views

headphone input to arduino for FFT usage

I am building a FFT audio-reactive project with an Arduino that I would like to add a line-in input to. I am most likely to be using a ATTiny84 or ATTiny85 as the sampling device, which is running at ...
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2answers
221 views

How to find the source of a noise in a particular band

The problem: The ADSL2+ service at home is not performing up to its potential. The modem is supposed to sync at 16 Mbps (downstream) but the it does only up to 11.5 Mbps. Using the diagnostic tools ...
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107 views

Frequency Response Function Estimate via FFT Question

I want to estimate the FRF of a dynamic LTI system given experimental input and output data. I know generally the approach is to use a chirp as an input to make sure enough frequency content is ...
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171 views

dsPIC33E ADC to FFT help

I am sampling an audio range signal with a bandwidth of 3100Hz and then applying a FFT using the DSP library example from Microchip to determine the most dominant frequency of the signal. On the last ...
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635 views

In LTspice can I convert the units of an FFT which by default seem to be shown in dBV to dBµV?

In LTspice can I convert the units of an FFT which by default seem to be shown in dBV to dBµV? Cause of reason: The reason for this is that I've a modeled a LISN in LTspice where I want to simulate ...
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185 views

Can the transient response of a system be calculated using FFT and inverse FFT?

I have a system, its input and output has the following relationship. I want to know the transient response of the system with respect to a ramping input Xi=t, by solving the differential equation, ...
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58 views

What could be the source of this noise?

Below is the output of an accelerometer when it is standing still: The zoomed 0.5 seconds of time series voltage data above is from a 4 seconds of measurement with a data acquisition board at 30kHz ...
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3answers
99 views

Why is the dB of the FFT plots exceeding 96dB for these signals sampled by an 16 bit ADC

There is a 16-bit data acquisition board and below is the recording of 120 seconds of voltage input at 500Hz sampling rate. The blue plot corresponds to the input voltage Vin and the green plot output ...
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70 views

How to change FFT spike to curve

The first picture is a part of my circuit and the voltage pass through the high filter circuit. The second picture shows an FFT spike which is obtained from the .csv file created by oscilloscope. I ...
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30 views

non-negative FFT spectrum, subtlety

definations \$x(t)\$ is a function of time. Physically, it can be voltage, displacement, magnetization and so on. It can be real, complex, vectors or more fancy numbers. \$C(t)\$ is the auto ...
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679 views

Interpretation of FFT FMCW Doppler radar results

After a lot of research and help from the users here, I managed to do some FFT and signal processing in my first time in my life :) I have got the following figure, which shows one peak frequency, ...

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